I'm not sure how you can structure this, but if you just put the money in an account for the kids, you can't really dictate how those funds are invested or spent.
Also, you have an adult, married son. So you would need to be extra careful with any funds that were place in his name. Depending upon the laws in his state, it could be subject to community property. (Although I can't remember if gifts are separate property.) I certainly wouldn't put it in an account with both of your childrens' names. That could get really, really messy.
I think with my adult son, I would see if he was interested in learning your trade and try to include him in the process. Pay him if he helps. If he isn't interested, or doesn't want to help, he's an adult and he can learn his own way.
Given all this, I think the better course is to set the money aside in an account in you and your wife's name with the idea that if your children come to you in the future and want to venture into this, then you would have the capital to help them get started. I just don't think that handing kids a chunk of money is a good idea. In general, people do better with money they have earned. Just my two cents.